In order to be able to force moisture and other contaminants
out of refrigerant circuit, compressed air and nitrogen (to
force moisture out of refrigerant circuit) are to be used.

For the most part, blowing through the refrigerant circuit
with compressed air and nitrogen requires significantly more
work than flushing with refrigerant R134a. As flushing with
refrigerant r134a cleans the components more efficiently, always
flush in case of a complaint (blowing through should only be
used for certain complaints and individual components).

Only individual components should be flushed if:

there is no possibility of flushing the refrigerant circuit
with refrigerant R134a.

dirt or other contaminants are located in individual
components of the circuit.

vacuum reading is not maintained on evacuating a leak-free
refrigerant circuit (pressure build-up due to moisture in
refrigerant circuit).

refrigerant circuit has been left open for longer than
normal (e.g. following an accident).

pressure and temperature measurements in the refrigerant
circuit indicate the likelihood of moisture.

stipulated by the vehicle-specific repair manual Heating &
Air Conditioning following replacement of certain components.

Note

Blowing compressed air and nitrogen through the refrigerant
circuit does not achieve the level of cleanliness as flushing
with refrigerant R134a. Flushing with refrigerant R134a loosens
the refrigerant oil and the components are then cleaner. Refer
to
→ Chapter „Refrigerant Circuit, Flushing (Cleaning) with
Refrigerant R134a“.

When blowing, working pressure must not exceed a maximum of
15 bar (218 psi), (also use a pressure reducer for compressed
air if necessary).

WARNING

Nitrogen can leak uncontrolled from the cylinder.

Make exclusive use of pressure reducers for nitrogen
cylinders (maximum work pressure 15 bar (218 psi)).

Use appropriate emissions extraction units to draw
off gas mixture escaping from components.

Restrictor, expansion valve, compressor, receiver and
reservoir cannot be flushed with compressed air and nitrogen.

–

Remove this dryer cartridge on condensers that have one
installed in the integrated receiver/dryer.

–

First blow out dirt with compressed air, then remove
moisture from components with nitrogen.

–

Connect adapter to connect the pressure hose to the
refrigerant circuit. Refer to
→ Chapter „Adapter for Assembling Flushing Circuit“
and Heating & Air Conditioning.

Note the following points to prevent oil and moisture from
entering the refrigerant circuit from the compressed air system.

The compressed air must be routed through a compressed air
purifier for cleaning and drying. Use is therefore to be made of
filter and dryer for compressed air (included in scope of
delivery as tool for painting work). Refer to the Workshop
Equipment And Special Tools Catalog.

For refrigerant lines with threads or union nut at
connection, make use of A/C Adapter Set - Adapter 1 -VAG1785/1-
through A/C Adapter Set - Adapter 8 -VAG1785/8- for connection
of 5/8" -18 UNF charging hoses. This adaptor is located in the
Refrigerant Circuits Adapter Set 1 -VAS6338/1- and Refrigerant
Circuits Adapter Set 2 -VAS6338/50-.

On refrigerant pipes without thread or union nut on the
connection, use adapter from Refrigerant Circuits Adapter Set 1
-VAS6338/1- or Refrigerant Circuits Adapter Set 2 -VAS6338/50-
or a commercially available pistol with rubber mouthpiece.

Note

Compressed air/nitrogen emerging from components is to be
drawn off by way of an appropriate system (e.g. workshop
extraction system).

Certain contaminants cannot be removed or can only be
removed insufficiently from the refrigerant circuit with
compressed air. These contaminants can only be removed by
flushing with refrigerant R134a. Refer to
→ Chapter „Refrigerant Circuit, Flushing (Cleaning) with
Refrigerant R134a“.

Note
For vehicles in which no adapters fit on to the refrigerant
pipes, for example, a blower pistol with rubber mouthpiece is to
be used to blow ...

Other materials:

Introduction
The purpose of this Repair Manual is to provide foremen and
mechanics with the basic knowledge needed to ensure expert
working.
Note
Expert knowledge is achieved by one who has taken part
successfully in instructiona ...